A rapid and economical model of chemotherapy for human solid tumor xenografts has been developed. Human cancer cell lines have been established in culture either directly from biopsy or surgical excision of tumors, or from transplantable tumors in nude mice. Antitumor agents, known and newly developed, will be evaluated for their antitumor activity and drug toxicity in anti-thymocyte serum (ATS) immunosuppressed mice bearing subcutaneously growing cell-line-derived human colon carcinomas (DLD-1, HCT-8, HCT-15, HRT-18), human lung carcinoma LX-1 and human breast carcinoma MDA-MD-231. A major goal is to see whether the ATS-model is predictive for clinical drug sensitivity. For those patients being treated with a particular chemotherapeutic agent(s), an effort will be made to obtain a subline resistant to that drug and the drug sensitivity of the resistant line will be studied. In addition, the biochemical action of effective agent(s) and mechanism of drug resistance will be studied.